Upgrading classical tuners is aggravating in my experience if you expect to use all of the pre-existing mounting holes in the peghead. There seems to be no standard for spacing between plate mounting holes.
I recently replaced mid-line Gotoh tuners with the premium model Gotoh tuners and only 2 of the 4 plate holes lined up. Same maker !
I happened to also have a set of Sloane tuners on hand and only one of the plate holes lined up with the Gotoh plate holes.
For the heck of it I tried matching up the new Sloane and Gotoh tuners with the pre-existing tuner mounting holes on three different guitars. Close on some, but a complete match on none.
Note: You may also have to do a tiny bit of sanding of the roller barrel holes for proper clearance. Although the on-center spacing between rollers on tuners seems to be standard, the diameters of the rollers can be different by a tiny amount on different tuners. They will fit, but you might experience some resistance when tuning. At least that is what I found.
Try to find out what tuners Martin will supply and then check dimensions on Stew Mac's website or on the manufacturers site. If you are lucky they might be there.
Good luck. Filling the old holes is not too bad of a job.In my case, all of the old holes are covered by the new mounting plate.
Mark
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